Base station apparatus, terminal apparatus, transmission method, and reception method

ABSTRACT

Disclosed is a base station apparatus in which a configuration section ( 102 ) configures, within a data assignable region for a terminal apparatus ( 200 ), a first search space and a second search space each being a candidate to which control information is assigned, each of the first search space and the second search space including a plurality of control channel elements, and a signal assignment section ( 105 ) assigns control information to each of the first search space and the second search space. In addition, the configuration section ( 102 ) allocates numbers to a plurality of first control channel elements included in the first search space in an ascending order, and allocates numbers larger than or identical with the numbers allocated to the first control channel elements to a plurality of second control channel elements included in the second search space.

TECHNICAL FIELD

The present invention relates to a base station apparatus, a terminalapparatus, a transmission method, and a reception method.

BACKGROUND ART

In recent years, accompanying the adoption of multimedia information incellular mobile communication systems, it has become common to transmitnot only speech data but also a large amount of data such as still imagedata and moving image data. Furthermore, studies are being activelyconducted in LTE-Advanced (Long Term Evolution Advanced) to realize hightransmission rates by utilizing broad radio bands, Multiple-InputMultiple-Output (MIMO) transmission technology, and interference controltechnology.

In addition, taking into consideration the introduction of variousdevices as radio communication terminals in M2M (machine to machine)communication and the like as well as an increase in the number ofmultiplexing target terminals due to MIMO transmission technology, thereis a concern regarding a shortage of resources in a region (that is, a“PDCCH region”) to which a PDCCH (Physical Downlink Control Channel) tobe used for a control signal is assigned. A DL grant (also referred toas “DL assignment”), which indicates a downlink (DL) data assignment,and a UL grant, which indicates an uplink (UL) data assignment, aretransmitted on a PDCCH. The DL grant notifies the terminal that aresource in the subframe in which the DL grant is transmitted has beenassigned to the terminal. The UL grant notifies that a resource in atarget subframe defined in advance by the UL grant has been assigned tothe terminal. If a control signal (PDCCH) cannot be assigned due to suchresource shortage of the PDCCH region, downlink data cannot be assignedto the terminals. Therefore, even if a resource region (i.e., a “PDSCH(Physical Downlink Shared Channel) region”) to which downlink data is tobe assigned is available, the resource region may not be used, whichcauses a decrease in the system throughput.

As a method for solving such resource shortage of the PDCCH region, astudy has been carried out on arranging, in a data region, controlsignals for radio terminal apparatuses (hereinafter, abbreviated as“terminal” and also referred to as “UE (User Equipment)”) served by aradio base station apparatus (hereunder, abbreviated as “base station”).A resource region in which control signals for terminals served by thebase station are assigned is referred to as an Enhanced PDCCH (ePDCCH)region, a New-PDCCH (N-PDCCH) region, an X-PDCCH region or the like.Assigning the control signal (i.e., ePDCCH) in a data region asdescribed above enables transmission power control on control signalstransmitted to a terminal near a cell edge or interference control forinterference by a control signal to another cell or interference fromanother cell to the cell provided by the base station.

A study has been carried out on assigning an ePDCCH to a logicalresource, which is referred to as eCCE (enhanced Control ChannelElements), and then assigning the ePDCCH to a physical resource (forexample, see FIG. 1). In the LTE and LTE-Advanced systems, one RB(resource block) has 12 subcarriers in the frequency domain and has awidth of 0.5 msec in the time region (for example, see NPL 1). A unit inwhich two RBs are combined in the time region is referred to as an RBpair (for example, see FIG. 1). That is, an RB pair has 12 subcarriersin the frequency domain, and has a width of 1 msec in the time region.When an RB pair represents a group of 12 subcarriers on the frequencyaxis, the RB pair may be referred to as simply “RB.” In addition, in aphysical layer, an RB pair is also referred to as a PRB pair (physicalRB pair). A resource element (RE) is a unit defined by a singlesubcarrier and a single OFDM symbol (see FIG. 1).

The number of eCCEs that are used to transmit the ePDCCH is referred toas an aggregation level. The base station determines the applicationlevel according to the channel quality between the base station and theterminal.

A set of assignment candidates (ePDCCH candidates) of a resource region,to which the ePDCCH is assigned, is referred to as a search space. Thesearch space for the ePDCCH is configured for an individual terminal byhigher layer signaling. As a method for higher layer signaling, a studyhas been carried out on designating the number of a PRB paircorresponding to the search space among the PRB pairs as a physicalresource unit. The terminal recognizes, as the search space of theterminal, PRB pairs that are identified by the PRB pair number notifiedby higher layer signaling, a configuration pattern (the aggregationlevel, the number of ePDCCH candidates of each aggregation level, ashift pattern, and the like) separately defined in advance. The terminalmonitors the search space of the terminal to detect an ePDCCH intendedfor the terminal.

“Localized assignment” that assigns ePDCCHs collectively at positionsclose to each other on the frequency band, and “distributed assignment”that assigns ePDCCHs by distributing the ePDCCHs on the frequency bandare being studied as assignment methods for ePDCCHs (for example, seeFIG. 1). Localized assignment is an assignment method for obtaining afrequency scheduling gain, and can be used to assign ePDCCHs toresources that have favorable channel quality based on channel qualityinformation. Distributed assignment distributes ePDCCHs on the frequencyaxis, and can obtain a frequency diversity gain. In the LTE-Advancedsystem, both a search space for localized assignment and a search spacefor distributed assignment may be configured.

In the localized assignment, each eCCE may be assigned in a unit inwhich a PRB pair is divided into four, three, or two eCCEs. In thelocalized assignment, when the aggregation level is equal to or largerthan 2, a plurality of eCCEs to which an ePDCCH is assigned are assignedto the same PRB pair. However, when the aggregation level is larger thanthe number of divisions of the PRB pair, the eCCEs are assigned to aplurality of PRB pairs.

In the distributed assignment, the eCCEs are assigned to a plurality ofPRB pairs. A resource (RE group) that is obtained by dividing a PRB pairis referred to as an eREG (enhanced Resource Element Group), and oneeCCE is assigned to a plurality of eREGs that belong to different PRBpairs. As a method of dividing a PRB pair into eREGs, there is a methodof dividing a PRB pair in subcarrier units, a method of generating anddividing a resource (RE) group, or the like. The number of divisions ofa PRB pair (the number of eREGs per PRB pair) may be 8, 12, 16, 24, 36,and the like (for example, see FIGS. 2A to 2C; when the number ofdivisions is 8, 16, and 36).

The base station can configure the search spaces of a plurality ofterminals in the same PRB pair. Since a minimum unit for transmitting anePDCCH becomes a resource region smaller than a PRB pair, the ePDCCHs ofa plurality of terminals are arranged in the same resource region or indifferent resource regions within the same PRB pair, thereby reducingthe number of PRB pairs for the ePDCCH and increasing the number of PRBpairs for data. Accordingly, there is a need for a method of configuringa search space that can be shared by a plurality of terminals.

In the LTE-Advanced, a study has been carried out on configuring aplurality of search spaces of ePDCCHs for each terminal. For example, asa case in which a plurality of search spaces of ePDCCHs are configuredfor each terminal, the following cases (1) to (3) can be identified.

(1) Common Search Space and UE Specific Search Space

A common search space that is used to transmit special control signalsand a UE specific search space into which a DL assignment and a UL grantof an individual terminal are transmitted are configured in eachterminal. The special control signals include system information,paging, RACH response, PUDCCH power control, PUDCCH power control, andthe like, and control signals masked with SI-RNTI, P-RNTI, RA-RNTI,TPC-PUCCH-RNTI, and TPC-PUSCH-RNTI are transmitted.

(2) Two UE Specific Search Space

Two UE specific search spaces (for example, search space 1 and searchspace 2) of each individual terminal are configured (for example, seeNPL 3). For example, the search space 1 is used for more robusttransmission than the search space 2. The robust transmission isattained by using a PRB pair in which interference control with othercells is performed, configuring the position of an ePDCCH candidatehaving a high aggregation level, configuring the position of an ePDCCHcandidate having a high frequency, space, or time diversity order, orthe like.

An operation becomes possible, where, by assigning the search space 1 ofthe two search spaces so as to be shared between a plurality ofterminals, when the number of terminals per subframe is small, only thesearch space 1 is used, and when the number of terminals increases, thesearch space 2 is further used. By adapting this configuration, when thenumber of terminals is small, it is possible to reduce the number of PRBpairs for an ePDCCH, thereby increasing the number of PRB pairs that canbe used for data transmission. At this time, the search space 2 variesfor each terminal and a terminal in which the search space 2 is used isselected to change the PRB pairs for the ePDCCH, thereby improvingflexibility of the use of the PRB pairs.

The search space 1 may be for distributed assignment, and the searchspace 2 may be for localized assignment. In this case, when thereliability of feedback information is high, the search space 2(localized assignment) is used, and PRB pairs having excellentcharacteristics inherent in the terminal can be assigned. Whenreliability of feedback information is low, switching to the use of thesearch space 1 (distributed assignment) is made to obtain the frequencydiversity gain, and the PRB pairs are shared with other terminals,thereby improving the utilization efficiency of the PRB pairs.

(3) Band Extension Function (CA: Carrier Aggregation) and Cross CarrierScheduling

The CA is a function that is newly introduced in the LTE-Advanced, andbrings a plurality of LTE system regions called component carriers (CC)together, thereby realizing improvement of the maximum transmission rate(see NPL 2). When a terminal uses a plurality of CCs, one CC isconfigured as a primary cell (PCell), and the remaining CCs areconfigured as secondary CCs (SCell). The configuration of the PCell andthe SCells may vary for each terminal. The cross carrier scheduling is aresource assignment method in which inter-cell interference control isperformed in a CC unit in a PDCCH. In the cross carrier scheduling, thebase station can transmit DL grants and UL grants of other CCs in thePDCCH region of a certain CC. If the cross carrier scheduling isapplied, the PDCCH is transmitted from different CCs between adjacentcells, thereby reducing inter-cell interference of the PDCCH.

During the CA operation, when the cross carrier scheduling isconfigured, controls signals for a plurality of CCs are collected intoone CC, and a plurality of search spaces corresponding to each of aplurality of CCs (PCell and SCells) are configured.

The cases (1) to (3) where a plurality of search spaces of ePDCCHs foreach terminal have been described.

In the LTE, as a feedback method (A/N mapping method) of a responsesignal (ACK/NACK signal, A/N signal) for downlink data assignment, A/Nmapping (PUCCH (Physical Uplink Control CHannel) format 1a: BPSK) duringone code word (CW) processing and A/N mapping (PUCCH format 1b: QPSK)during 2CW processing are adopted.

When a DL assignment is transmitted using a PDCCH, a resource (PUCCHresource) of the PUCCH is defined in association with a CCE index of afirst CCE among CCEs (Control Channel Element) as a resource used totransmit the DL assignment on a one-to-one basis. The PUCCH resource iscalled an implicit resource. The CCEs are resources that are generatedby dividing the resource (PDCCH resource) of the PDCCH, and are attachedwith CCE indexes that do not overlap each other. A CCE index isrecognized commonly between terminals within a cell.

The DL assignment and the UL grant are assigned to one CCE (Aggregationlevel: 1) or a plurality of CCEs (Aggregation level: 2, 4, 8) accordingto the aggregation level to be set. When control information is assignedto a plurality of CCEs, the control information is assigned to CCEshaving continuous CCE indexes.

In the LTE, the PDCCH is demodulated with a CRS (Cell-specific ReferenceSignal) as a reference signal. An antenna port of a CRS to be used iscommon between terminals within a cell. Accordingly, it is difficult toapply MU-MIMO (Multi user MIMO) in which a plurality of DL assignmentsor UL grants are transmitted by the same CCE.

Since one PDCCH region is configured per cell, there is no case wherethe CCE indexes of the CCEs to which the DL assignment and the UL grantare assigned overlap between terminals within a cell. That is, when aterminal within the cell uses the PDCCH region, it is designed such thatthere is no collision of the PUCCH resources associated with the CCEindexes.

However, exceptionally, when the PUCCH is transmitted through twoantenna ports and when channel selection is applied to the PUCCH, twoPUCCH resources are implicitly designated from the CCE indexes that areused for one DL assignment. For example, PUCCH resources respectivelyassociated with first CCE index #N and next CCE index #N+1 are used.Here, if the DL assignment of the other terminal is assigned using theCCE of CCE index #N+1, there is collision of the PUCCH resources thatare used between terminals. The base station does not use CCE index #N+1for a DL assignment or a UL grant is assigned to CCE index #N+1, therebyavoiding collision of the PUCCH resources. Since there are many caseswhere a DL assignment that indicates transmission of two CWs has anaggregation level equal to or larger than 2, collision of the PUCCHresources does not become a significant problem as much. In this way, inthe PDCCH, since there is no case where the CCE indexes to be usedcollide within the same cell, collision of the PUCCH resources does notbecome a major problem.

CITATION LIST Non-Patent Literature

NPL 1

-   3GPP TS 36.211 V10.4.0, “Physical Channels and Modulation”    NPL 2-   3GPP TS 36.213 V10.4.0, “Physical layer procedures”    NPL 3-   R1-122979, “Way forward on ePDCCH search space”

SUMMARY OF INVENTION Technical Problem

In the above-described ePDCCH, similarly to the PDCCH, a study has beencarried out on implicit assignment in which the eCCE indexes and thePUCCH resources are associated with each other on a one-to-one basis(for example, see FIG. 3).

However, as described above, an ePDCCH search space may be configuredfor an individual terminal by higher layer signaling. Accordingly, theeCCE index corresponding to the PRB pair number indicated as the ePDCCHsearch space may vary for each terminal. Although the associationbetween the eCCE indexes and the PUCCH resources is shared between theterminals, if the eCCE index corresponding to the PRB pair number variesbetween the terminals, in the implicit assignment of the eCCE indexesand the PUCCH resources, the PUCCH resources may collide due tocollision of the eCCE indexes.

FIG. 4 illustrates an example in which PUCCH resources collide due tocollision of the eCCE indexes. In FIG. 4, localized assignment isapplied to an ePDCCH, and a search space 1 (SS1) and a search space 2(SS2) are configured in UE1 and UE2. The search space 1 is shared by UE1and UE2 and assigned to PRB pairs #2, #8, #14, and #20. The search space2 of UE1 is assigned to PRB pairs #0, #1, #22, and #23, and the searchspace 2 of UE2 is assigned to PRB pairs #3, #9, #15, and #21. In FIG. 4,four CCEs are assigned per PRB pair.

The terminals (UE1 and UE2) allocate the eCCE indexes in an ascendingorder of the PRB pair numbers corresponding to the search space set ineach terminal. Accordingly, UE1 recognizes that the ePDCCH addressed toUE1 is likely to be transmitted to PRB pairs #0, #1, #2, #8, #14, #20,#22, and #23, and allocates the eCCE indexes (CCE #0 to CCE #31) in anorder of PRB pairs #0, #1, #2, #8, #14, #20, #22, and #23. Similarly,UE2 allocates the eCCE indexes (CCE #0 to CCE #31) in an order of PRBpairs #2, #3, #8, #9, #14, #15, #20, and #21. As illustrated in FIG. 4,the eCCE index corresponding to the same PRB pair number may varybetween UE1 and UE2. That is, the PRB pair number corresponding to thesame eCCE index may vary between UE1 and UE2.

For example, in FIG. 4, while eCCE #12 of UE1 is assigned to PRB pair#8, eCCE #12 of UE2 is assigned to PRB pair #9. Accordingly, the basestation can simultaneously transmit the ePDCCH to both UE1 and UE2 usingeCCE #12. However, in UE1 and UE2, since the same PUCCH resource (inFIG. 3, PUCCH #12) associated with eCCE #12 is used, there is collisionof the PUCCH resources between UE1 and UE2. Therefore, in FIG. 4, inorder to simultaneously use eCCE #12 for UE1 and UE2, it is necessary toassociate different PUCCH resources with eCCE #12 to be used by UE1 andeCCE #12 to be used by UE2.

In this way, when a plurality of ePDCCH search spaces are configured forone terminal, in order to avoid collision of the PUCCH resources to beused between terminals, the number of PUCCH resources increases. Forthis reason, in the uplink, the number of resources (PUSCH resources)that can be used to transmit uplink data (PUSCH) is reduced, and uplinkthroughput is reduced.

An object of the present invention is to provide a base stationapparatus, a terminal apparatus, a transmission method, and a receptionmethod capable of avoiding collision of PUCCH resources betweenterminals while limiting an increase in the number of PUCCH resourceseven when a plurality of search spaces are configured with respect to anePDCCH for a single terminal.

Solution to Problem

A base station apparatus according to an aspect of the present inventionincludes: a configuration section that configures, within a dataassignable region for a terminal apparatus, a first search space and asecond search space each being a candidate to which control informationis assigned, each of the first search space and the second search spaceincluding a plurality of control channel elements; and a transmissionsection that transmits the control information assigned to each of thefirst search space and the second search space, in which: a number of acontrol channel element to which the control information is assigned isassociated on a one-to-one basis with an uplink resource to be used totransmit a response signal to downlink data; and the configurationsection allocates numbers to a plurality of first control channelelements included in the first search space in an ascending order, andallocates numbers larger than or identical with the numbers allocated tothe first control channel elements to a plurality of second controlchannel elements included in the second search space.

A terminal apparatus according to an aspect of the present inventionincludes: a configuration section that configures, within a dataassignable region, a first search space and a second search space eachbeing a candidate to which control information is assigned, each of thefirst search space and the second search space including a plurality ofcontrol channel elements; and a reception section that receives thecontrol information assigned to each of the first search space and thesecond search space, in which: a number of a control channel element towhich the control information is assigned is associated on one-to-onebasis with an uplink resource to be used to transmit a response signalto downlink data; and the configuration section allocates numbers to aplurality of first control channel elements included in the first searchspace in an ascending order, and allocates numbers larger than oridentical with the numbers allocated to the first control channelelements to a plurality of second control channel elements included inthe second search space.

A transmission method according to an aspect of the present inventionincludes: configuring, within a data assignable region for a terminalapparatus, a first search space and a second search space each being acandidate to which control information is assigned, each of the firstsearch space and the second search space including a plurality ofcontrol channel elements; and transmitting the control informationassigned to each of the first search space and the second search space,in which: a number of a control channel element to which the controlinformation is assigned is associated on a one-to-one basis with anuplink resource to be used to transmit a response signal to downlinkdata; and numbers are allocated to a plurality of first control channelelements included in the first search space in an ascending order, andnumbers larger than or identical with the numbers allocated to the firstcontrol channel elements are allocated to a plurality of second controlchannel elements included in the second search space.

A reception method according to an aspect of the present inventionincludes: configuring, within a data assignable region for a terminalapparatus, a first search space and a second search space each being acandidate to which control information is assigned, each of the firstsearch space and the second search space including a plurality ofcontrol channel elements; and receiving the control information assignedto each of the first search space and the second search space, in which:a number of a control channel element to which the control informationis assigned is associated on a one-to-one basis with an uplink resourceto be used to transmit a response signal to downlink data; and numbersare allocated to a plurality of first control channel elements includedin the first search space in an ascending order, and numbers larger thanor identical with the numbers allocated to the first control channelelements are allocated to a plurality of second control channel elementsincluded in the second search space.

Advantageous Effects of Invention

According to the present invention, even when a plurality of searchspaces are configured with respect to an ePDCCH for a single terminal,it is possible to avoid collision of PUCCH resources between terminalswhile limiting an increase in the number of PUCCH resources.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram provided for describing an eCCE and a PRB pair;

FIGS. 2A to 2C are diagrams each illustrating a configuration example ofan eREG;

FIG. 3 is a diagram illustrating association of eCCE indexes and PUCCHresources;

FIG. 4 is a diagram provided for describing a problem in acorrespondence relationship of an eCCE index and a PRB pair between aplurality of terminals;

FIG. 5 is a block diagram illustrating main components of a base stationaccording to Embodiment 1 of the present invention;

FIG. 6 is a block diagram illustrating main components of a terminalaccording to Embodiment 1 of the present invention;

FIG. 7 is a block diagram illustrating the configuration of the basestation according to Embodiment 1 of the present invention;

FIG. 8 is a block diagram illustrating the configuration of the terminalaccording to Embodiment 1 of the present invention;

FIG. 9 is a diagram illustrating a search space configuration exampleaccording to Embodiment 1 of the present invention;

FIG. 10 is a diagram illustrating a search space configuration exampleaccording to Embodiment 2 of the present invention;

FIG. 11 is a diagram illustrating another search space configurationexample according to Embodiment 2 of the present invention;

FIG. 12 is a diagram illustrating an example of distributed assignmentof an ePDCCH (the number of divisions of a PRB pair: 8);

FIG. 13 is a diagram illustrating an example of distributed assignmentof an ePDCCH (the number of divisions of a PRB pair: 16);

FIG. 14 is a diagram illustrating a search space configuration exampleaccording to Embodiment 3 of the present invention (the number ofdivisions of a PRB pair: 8);

FIG. 15 is a diagram illustrating a search space configuration exampleaccording to Embodiment 3 of the present invention (the number ofdivisions of a PRB pair: 16);

FIGS. 16A and 16B are diagrams provided for describing a problem of eCCEassignment in a PRB pair according to Embodiment 4 of the presentinvention;

FIGS. 17A and 17B are diagrams illustrating a search space configurationexample according to Embodiment 4 of the present invention (the numberof divisions of a PRB pair: 16);

FIGS. 18A and 18B are diagrams illustrating a search space configurationexample according to Embodiment 4 of the present invention (the numberof divisions of a PRB pair: 8); and

FIGS. 19A and 19B are diagrams illustrating another search spaceconfiguration example according to Embodiment 4 of the presentinvention.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention are described in detail hereunderwith reference to the accompanying drawings. Throughout the embodiments,the same elements are assigned the same reference numerals, and aduplicate description of the elements is omitted.

Embodiment 1 Communication System Overview

A communication system according to the present embodiment has basestation 100 and terminal 200. The communication system is, for example,an LTE-Advanced system. Base station 100 is, for example, a base stationthat supports the LTE-Advanced system, and terminal 200 is, for example,a terminal that supports the LTE-Advanced system.

Although base station 100 and terminal 200 can perform transmission andreception of control information (DL assignment or UL grant) using aPDCCH region or an ePDCCH region, in the following description, forsimplification of description, only transmission and reception ofcontrol information in an ePDCCH region will be described.

FIG. 5 is a block diagram illustrating main components of base station100 according to the present embodiment.

In base station 100, configuration section 102 configures a first searchspace and a second search space as candidates, to which controlinformation is assigned, within a data assignable region (PDSCH region)for terminal 200. Each of the first search space and the second searchspace includes a plurality of control channel elements (eCCEs).

Signal assignment section 105 assigns the control information (DLassignment or UL grant) to each of the first search space and the secondsearch space configured by configuration section 102. Accordingly, thecontrol information assigned to each of the first search space and thesecond search space is transmitted.

FIG. 6 is a block diagram illustrating main components of terminal 200according to the present embodiment.

In terminal 200, configuration section 205 configures a first searchspace and a second search space as candidates, to which controlinformation is assigned, within a data assignable region (PDSCH region).

Control signal reception section 206 extracts the control informationassigned to each of the first search space and the second search spaceconfigured by configuration section 205. Accordingly, the controlinformation transmitted from base station 100 is received.

In base station 100 and terminal 200, the number (eCCE index) of acontrol channel element to which the control information is assigned isassociated with an uplink resource (PUCCH resource) to be used totransmit a response signal to downlink data (PDCCH) on a one-to-onebasis. Configuration section 102 and configuration section 205 allocatenumbers to a plurality of first control channel elements included in thefirst search space in an ascending order, and allocate numbers largerthan or identical with the numbers allocated to the plurality of firstcontrol channel elements to a plurality of second control channelelements included in the second search space.

[Configuration of Base Station 100]

FIG. 7 is a block diagram illustrating the configuration of base station100 according to the present embodiment. As illustrated in FIG. 7, basestation 100 includes assignment information generation section 101,configuration section 102, error correction coding section 103,modulation section 104, signal assignment section 105, transmissionsection 106, reception section 107, demodulation section 108, errorcorrection decoding section 109, and A/N signal demodulation section110.

In a case where there is a downlink data signal (DL data signal) to betransmitted and an uplink data signal (UL data signal) to be assigned toan uplink (UL), assignment information generation section 101 determinesresources (RB) to which assign the data signals are assigned, andgenerates assignment information (DL assignment and UL grant). The DLassignment includes information relating to assignment of the DL datasignal. The UL grant includes information relating to allocatedresources for the UL data signal to be transmitted from terminal 200.The DL assignment is outputted to signal assignment section 105, and theUL grant is outputted to signal assignment section 105 and receptionsection 107.

Configuration section 102 configures one or a plurality of ePDCCH searchspaces for each terminal 200. Specifically, configuration section 102configures a PRB pair number in which an ePDCCH search space isarranged, an eCCE index of each aggregation level, and an assignmentmethod (localized assignment or distributed assignment) of the searchspace (ePDCCH) for each terminal 200. The ePDCCH search space includes aplurality of assignment candidates (ePDCCH candidates). Each “assignmentcandidate” includes eCCEs corresponding to the number of aggregationlevels. In the localized assignment, eCCEs are obtained by dividing eachPRB pair into a predetermined number of parts (for example, 4divisions). In the distributed assignment, in order to assign eCCEs to aplurality of PRB pairs, one CCE is assigned to a plurality of eREGs(resources obtained by dividing a PRB pair) that belong to different PRBpairs.

When a plurality of ePDCCH search spaces are configured for terminal200, configuration section 102 assigns an eCCE index to each searchspace. When the same PRB pair numbers are assigned to a plurality ofsearch spaces, configuration section 102 allocates an eCCE index of adifferent search space to the PRB pair according to an eCCE index of asearch space having a small search space number. Details of a searchspace configuration method in configuration section 102 will bedescribed below.

Configuration section 102 outputs information relating to a configuredsearch space (hereinafter, may also be referred to as “search spaceinformation”) to signal assignment section 105. The search spaceinformation includes, for example, the PRB pair number, the eCCE index,the ePDCCH assignment method, and the like. Configuration section 102outputs information regarding the PRB pair configured in the searchspace and information regarding the ePDCCH assignment method to errorcorrection coding section 103 as control information. When the localizedassignment or the distributed assignment is configured in advance as theePDCCH assignment method, information regarding the ePDCCH assignmentmethod is not required.

Error correction coding section 103 receives a transmission data signal(DL data signal) and control information received from configurationsection 102 as input signals, performs error correction coding on theinput signals, and outputs the processed signals to modulation section104.

Modulation section 104 modulates the signals received from errorcorrection coding section 103, and outputs the modulated data signal tosignal assignment section 105.

Signal assignment section 105 assigns the assignment information (DLassignment and UL grant) received from assignment information generationsection 101 to any CCE among eCCEs (eCCEs in assignment candidate units)corresponding to a PRB pair number indicated by search space informationreceived from configuration section 102. Signal assignment section 105also assigns the data signal received from modulation section 104 to adownlink resource corresponding to the assignment information (DLassignment) received from assignment information generation section 101.

A transmission signal is formed by assignment information and a datasignal being assigned to predetermined resources in this manner. Thethus-formed transmission signal is outputted to transmission section106. Signal assignment section 105 notifies reception section 107 of aneCCE index of an eCCE used to transmit the DL assignment.

Transmission section 106 executes radio transmission processing such asup-conversion on the input signal, and transmits the obtained signal toterminal 200 via an antenna.

Reception section 107 receives a signal transmitted from terminal 200via an antenna, and outputs the received signal to demodulation section108. More specifically, reception section 107 separates a signalcorresponding to a resource indicated by a UL grant received fromassignment information generation section 101 from the received signal,and executes reception processing such as down-conversion on theseparated signal and thereafter outputs the obtained signal todemodulation section 108. Reception section 107 separates a signal thatcorresponds to a PUCCH resource associated with an eCCE index receivedfrom signal assignment section 105 and outputs the separated signal toA/N signal demodulation section 110.

Demodulation section 108 executes demodulation processing on the inputsignal, and outputs the obtained signal to error correction decodingsection 109.

Error correction decoding section 109 decodes the input signal to obtainthe received data signal from terminal 200.

A/N signal demodulation section 110 performs modulation processing onthe signal received from reception section 107, performs A/Ndetermination processing (determination on ACK or NACK) on the obtainedA/N signal, and outputs the determination result.

[Configuration of Terminal 200]

FIG. 8 is a block diagram illustrating the configuration of terminal 200according to the present embodiment. As illustrated in FIG. 8, terminal200 includes reception section 201, signal separation section 202,demodulation section 203, error correction decoding section 204,configuration section 205, control signal reception section 206, errorcorrection coding section 207, modulation section 208, signal assignmentsection 209, and transmission section 210.

Reception section 201 receives a signal transmitted from base station100 via an antenna, and after executing reception processing such asdown-conversion thereon, outputs the processed signal to signalseparation section 202.

Signal separation section 202 extracts a control signal relating toresource allocation from the reception signal received from receptionsection 201, and outputs the extracted signal to control signalreception section 206. Signal separation section 202 also extracts fromthe reception signal a signal corresponding to a data resource (that is,a DL data signal) indicated by the DL assignment output from controlsignal reception section 206, and outputs the extracted signal todemodulation section 203.

Demodulation section 203 demodulates the signal outputted from signalseparation section 202, and outputs the demodulated signal to errorcorrection decoding section 204.

Error correction decoding section 204 decodes the demodulated signaloutputted from demodulation section 203, and outputs the obtainedreceived data signal. In particular, error correction decoding section204 outputs “information relating to PRB pairs configured in a searchspace” transmitted as a control signal from base station 100, toconfiguration section 205. Error correction decoding section 204determines whether or not an error is included in a received data signalafter decoding using CRC (Cyclic Redundancy Check) and generates an A/Nsignal that represents the determination result (ACK or NACK). The A/Nsignal is output to signal assignment section 209.

Configuration section 205 identifies a search space configured forterminal 200 of configuration section 205 that uses an ePDCCH. Forexample, first, based on information received from error correctiondecoding section 204, configuration section 205 identifies PRB pairs tobe configured in the search space. Next, configuration section 205determines an eCCE index of a search space corresponding to the PRBpairs. At this time, when a plurality of ePDCCH search spaces areconfigured, configuration section 205 allocates an eCCE index to eachsearch space. When the same PRB pair number is assigned to a pluralityof search spaces, configuration section 205 allocates a CCE index of adifferent search space to the PRB pair according to an eCCE index of asearch space having a small search space number. Configuration section205 identifies which eCCE index is configured in an ePDCCH candidate foreach aggregation level according to a common rule between base station100 defined for each terminal 200 in advance and terminal 200. Forexample, configuration section 205 determines an eCCE index as an ePDCCHcandidate of each aggregation level based on a UE ID (an ID of anindividual terminal). Next, search space configuration section 205outputs information relating to PRB pairs and CCEs configured as thesearch space to control signal reception section 206. The details of asearch space configuration method in configuration section 205 will bedescribed below in detail.

In a signal component received from signal separation section 202,control signal reception section 206 detects a control signal (DLassignment or UL grant) intended for terminal 200 of signal separationsection 202 by performing blind decoding with respect to CCEscorresponding to PRB pairs indicated by information received fromconfiguration section 205. That is, control signal reception section 206receives a control signal assigned to one assignment candidate among aplurality of assignment candidates forming a search space configured byconfiguration section 205. Control signal reception section 206 outputsa detected DL assignment intended for terminal 200 of control signalreception section 206 to signal separation section 202, and outputs adetected UL grant intended for terminal 200 thereof to signal assignmentsection 209. Control signal reception section 206 outputs an eCCE indexof an eCCE with the detected DL assignment to signal assignment section209.

When a transmission data signal (UL data signal) is inputted to errorcorrection coding section 207, error correction coding section 207performs error correction coding on the transmission data signal andoutputs the obtained signal to modulation section 208.

Modulation section 208 modulates the signal received from errorcorrection coding section 207, and outputs the modulated signal tosignal assignment section 209.

Signal assignment section 209 assigns the signal outputted frommodulation section 208 according to the UL grant received from controlsignal reception section 206, and outputs the obtained signal totransmission section 210. Signal assignment section 209 assigns the A/Nsignal received from error correction decoding section 204 to apredetermined resource. Specifically, when there is a transmission datasignal, signal assignment section 209 multiplexes the A/N signal to thetransmission data signal, and outputs the obtained signal totransmission section 210. When there is no transmission data signal,signal assignment section 209 identifies a PUCCH resource based on aneCCE index received from control signal reception section 206, assignsthe A/N signal to the identified PUCCH resource, and outputs the A/Nsignal to transmission section 210.

Transmission section 210 executes transmission processing such asup-conversion on the input signal, and transmits the obtained signal.

[Operations of Base Station 100 and Terminal 200]

Operations of base station 100 and terminal 200 that have the aboveconfigurations will be described.

Base station 100 and terminal 200 configure a plurality of search spaces(for example, search space 1 and search space 2) as candidates, to whicha control signal addressed to terminal 200 is assigned, in an ePDCCHregion for one terminal 200. At this time, base station 100 and terminal200 allocate eCCE indexes (numbers) to a plurality of eCCEs included inthe search space 1 in an ascending order, and allocate numbers largerthan a plurality of eCCE indexes of the search space 1 to a plurality ofeCCEs included in the search space 2.

As described above, the eCCE indexes to which the control informationare assigned are associated with the PUCCH resources to be used totransmit the A/N signal to downlink data indicated to assign by thecontrol information on a one-to-one basis (see FIG. 3).

The search space 1 is a search space that is often shared betweenterminals 200. For example, the search space 1 is a search space (commonsearch space described above) that is often shared between a pluralityof terminals 200. The search space 1 and the search space 2 are UEspecific search spaces that are individually configured in respectiveterminals 200, and the search space 1 is a search space (search space tobe primarily used) with priority over the search space 2. When terminal200 performs communication using a plurality of CCs having PCell andSCell, the search space 1 is a search space to which control informationfor PCell is assigned, and the search space 2 is a search space to whichcontrol information for SCell is assigned.

FIG. 9 illustrates a search space configuration method in the presentembodiment. In FIG. 9, similarly to FIG. 4, localized assignment isapplied to an ePDCCH, and a search space 1 (SS1) and a search space 2(SS2) are respectively configured in terminals 200 (UE1 and UE2). Thesearch space 1 is shared by UE1 and UE2 and is assigned to PRB pairs #2,#8, #14, and #20. The search space 2 of UE1 is assigned to PRB pairs #0,#1, #22, and #23, and the search space 2 of UE2 is assigned to PRB pairs#3, #9, #15, and #21. However, each terminal 200 recognizes only thesearch space of terminal 200. In FIG. 9, four eCCEs are assigned per PRBpair.

Base station 100 and each terminal 200 (UE1 and UE2) first determine theeCCE indexes of the search space 1 among the search spaces configured inrespective terminal 200, and then determine the eCCE indexes of thesearch space 2. That is, base station 100 and each terminal 200 firstallocate the eCCE indexes in an ascending order of the PRB pair numberscorresponding to the search space 1, and then allocate the eCCE indexesin an ascending order of the PRB pair numbers corresponding to thesearch space 2.

Accordingly, UE1 and UE2 first allocate eCCE #0 to eCCE #15 to thesearch space 1. With this, eCCE #0 to eCCE #15 are assigned in an orderof the PRB pairs #2, #8, #14, and #20 corresponding to the search space1.

Next, UE1 and UE2 allocate eCCE #16 to eCCE #31 to the search space 2.With this, eCCE #16 to eCCE #31 are assigned in an order of the PRBpairs #0, #1, #22, and #23 corresponding to the search space 2 of UE1.Furthermore, eCCE #16 to eCCE #31 are assigned in an order of PRB pairs#3, #9, #15, and #21 corresponding to the search space 2 of UE2. Thatis, UE1 and UE2 allocate the eCCE indexes larger than the eCCE indexesof the search space 1 to the search space 2.

In this way, in the search space 1 that is shared by both UE1 and UE2,the eCCE indexes of the eCCEs that are assigned to PRB pairs #2, #8,#14, and #20 are the same between UE1 and UE2. That is, in the searchspace 1, since the association of the PRB pair numbers and the eCCEindexes matches each other in UE1 and UE2, and the use of eCCEs in UE1and UE2 matches the use of the PUCCH resource associated with the eCCEindexes. Accordingly, by taking into consideration only collision of theeCCEs, base station 100 can assign an ePDCCH addressed to UE1 and anePDCCH for UE2 to the shared search space 1 while avoiding collision ofthe PUCCH resources between UE1 and UE2, thereby facilitatingscheduling.

As described above, in the present embodiment, when a plurality ofsearch spaces are configured for each terminal 200, the eCCE indexesthat are continuous within the search space are allocated to at leastone search space (search space 1). With this, even the search spaceconfiguration is recognized between terminals 200, the same eCCE indexis easily allocated to the same (common) search space between terminals200. In other words, different eCCE indexes are not easily allocated tothe same (common) search space between terminals 200.

As described above, if different eCCE indexes are allocated to a searchspace that is shared between terminals 200, the correspondencerelationship of the eCCE indexes and the PRB pairs varies for eachterminal 200, and collision of the PUCCH resources and an increase inthe number of required resources occur (for example, see FIG. 4).

In contrast, in the present embodiment, the continuous eCCE indexes areallocated to at least one search space (search space 1), and the eCCEindexes larger than the eCCE indexes of at least one search space areallocated to the other search space (search space 2). With this, thecorrespondence of the eCCE indexes and the PRB pairs in the search space1 matches between terminals 200 that shares the search space 1regardless of the assignment of the eCCE indexes of the other searchspace 2. That is, in regard to the search space 1, collision of the eCCEindexes and collision of the PUCCH resources are aligned. Accordingly,base station 100 performs scheduling taking into consideration onlycollision of the eCCE indexes between terminals 200. Therefore, it ispossible to avoid collision of the PUCCH resources between terminals200.

Since collision of the eCCEs and collision of the PUCCH resources in thesearch space 1 match each other between terminals 200, the number ofPUCCH resources required for the search space 1 does not become largerthan the number of eCCE indexes of the search space 1. That is, it ispossible to limit an increase in the number of PUCCH resources.

Accordingly, according to the present embodiment, even when a pluralityof search spaces are configured with respect to an ePDCCH for a singleterminal, it is possible to avoid collision of the PUCCH resourcesbetween the terminals while limiting an increase in the number of PUCCHresources.

If different eCCE indexes are allocated to a search space that is sharedbetween terminals 200, the eCCE indexes corresponding to the same PRBpair may vary between terminals 200. For example, in FIG. 4, while theeCCE indexes corresponding to PRB pair #20 are eCCEs #20 to #23 in UE1,in UE2, the eCCE indexes corresponding to PRB pair #20 are eCCEs #24 to#27. In this case, if eCCE #20 is used in an ePDCCH for UE1, since thePUCCH resource associated with eCCE #20 is used, if eCCE #20 is used forUE2, collision of the PUCCH resources occurs. If eCCE #20 is used in anePDCCH for UE1, eCCE #24 cannot be used in an ePDCCH for UE2 that isassigned to the same PRB pair #20. For this reason, the PUCCH resourceassociated with eCCE #24 is not used and wasted. That is, in FIG. 4,there are a plurality of eCCE indexes that cannot be simultaneously usedbetween terminals 200.

In contrast, in the present embodiment, as described above, thecorrespondence of the eCCE indexes and the PRB pairs in the search space1 matches between terminals 200 that shares the search space 1.Accordingly, according to the present embodiment, there is nocombination of the eCCE indexes which cannot be simultaneously usedbetween terminals 200.

According to the present embodiment, the eCCE indexes for the searchspace 1 are aligned in the terminal 200, and in regard to the eCCEindexes for the search space 2 of each terminal 200, the eCCE indexesdifferent from the eCCE indexes for the search space 1 are allocated.Accordingly, it is possible to avoid collision of the eCCEs of thesearch space 1 and the search space 2 between terminals 200.

According to the present embodiment, even if the search space 1 that isconfigured in each terminal 200 is not notified to other terminals 200,the search space 1 to which the same eCCE index is allocated can beshared between terminals 200.

Embodiment 2

In the present embodiment, a case where some of a plurality of searchspaces configured in one terminal 200 is assigned to the same PRB pairin an overlapping manner will be described. A base station and aterminal according to the present embodiment share the same basicconfiguration as base station 100 and terminal 200 according toEmbodiment 1. Accordingly, description will be provided referring backto FIGS. 7 and 8.

A study has been carried out on varying an eCCE to be used in an ePDCCHcandidate according to an aggregation level. Accordingly, within asearch space, all eCCEs corresponding to a PRB pair number indicatedfrom a higher layer are not used as ePDCCH candidate. Therefore, thesame PRB pair is shared between a plurality of search spaces, and aplurality of eCCEs corresponding to different resources within the samePRB pair are added as an ePDCCH candidate, thereby reducing theprobability (blocking probability) of collision against the eCCEs ofother terminals 200 while maintaining the number of ePDCCH candidatesfor terminal 200. The same PRB pair is shared between a plurality ofsearch spaces, thereby reducing the total number of PRB pairs that areassigned to the search space of the ePDCCH and securing a larger numberof PUSCH regions. For this reason, throughput in the uplink can beimproved.

In the present embodiment, when some of a plurality of search spacesconfigured for one terminal 200 is assigned to the same PRB pair in anoverlapping manner, in the PRB pair to which a plurality of searchspaces are assigned, the eCCE indexes of other search spaces areallocated according to the eCCE index of a search space having a smallsearch space number. For example, when the search space 1 and the searchspace 2 are assigned to the same PRB pair with respect to terminal 200,in the PRB pair, the eCCE index of the search space 2 become identicalwith the eCCE index of the search space 1.

FIG. 10 illustrates an assignment example of eCCEs when the search space1 (SS1) and the search space 2 (SS2) are configured for one terminal200. In FIG. 10, PRB pair #20 is assigned in common to the search space1 and the search space 2. In FIG. 10, similarly to FIG. 9, base station100 and terminal 200 allocate the eCCE indexes (eCCEs #0 to #15) in anascending order in the search space 1. Accordingly, in the search space1, eCCEs #12 to #15 are assigned to PRB pair #20.

Base station 100 and terminal 200 allocate eCCE indexes #12 to #15 asthe eCCE indexes corresponding to PRB pair #20 in the search space 2according to the eCCE indexes of the search space 1. Terminal 200allocates the eCCE indexes other than the eCCE indexes corresponding toPRB pair #20 in the search space 2 in an ascending order. Accordingly,in the search space 2, eCCE #16 to eCCE #26 are assigned to PRB pairs #0and #1, eCCEs #12 to #15 are assigned to PRB pair #20, and eCCEs #24 to#27 are assigned to PRB pair #23.

That is, base station 100 and terminal 200 allocate the same eCCEindexes as specific eCCEs to eCCEs, which are assigned to the same PRBpair as specific eCCEs among a plurality of eCCEs of the search space 1,among a plurality of eCCEs of the search space 2. Base station 100 andterminal 200 allocate the eCCE indexes larger than the eCCE indexes ofthe search space 1 to the eCCEs other than the eCCEs, to which the sameeCCE indexes as the specific eCCEs are allocated, in the search space 2.

With this, as in Embodiment 1 (FIG. 9), it is possible to reduce thetotal number of eCCE indexes to be configured in terminal 200 whilematching the eCCE indexes in the search space 1 (that is, a search spacethat is easily shared with other terminals 200) between terminals 200that share the search space 1. For example, in Embodiment 1 (FIG. 9),while 32 eCCE indexes are allocated to UE1, in the present embodiment(FIG. 10), 28 eCCE indexes are allocated to UE1. That is, in FIG. 10, itis possible to reduce the number of eCCE indexes to be used in UE1 byfour compared to FIG. 9. Accordingly, since it is possible to reduce thenumber of PUCCH resources that are associated with the eCCEs, throughputin the uplink is improved.

According to the present embodiment, as the PRB pair is shared by thesearch space 1 and the search space 2, it is possible to reduce the PRBpairs that are assigned as a search space for terminal 200. For example,in Embodiment 1 (FIG. 9), while 8 PRB pairs are assigned to UE1, in thepresent embodiment (FIG. 10), 7 PRB pairs smaller than in Embodiment 1by one are assigned to UE1. Accordingly, in the present embodiment,since it is possible to secure a larger number of PUCCH regions comparedto Embodiment 1, throughput in the uplink is improved.

Instead of the eCCE assignment illustrated in FIG. 10, base station 100and terminal 200 may allocate the eCCE indexes for the search space 1and the search space 2 in the same manner as FIG. 9, and then may changeonly the eCCE indexes in the search space 2 corresponding to the PRBpair assigned in common to both search spaces to the eCCE indexes of thesearch space 1. For example, as illustrated in FIG. 11, first, eCCEs #16to #31 are allocated to the search space 2 in an ascending order in thesame manner as FIG. 9. Next, only portions of eCCEs #24, #25, #26, and#27 corresponding to PRB pair #20 are changed to eCCEs #12, #13, #14,and #15 corresponding to PRB pair #20 of the search space 1.

With this, in terminal 200, the PUCCH resources corresponding to eCCEs#24, 25, 26, and 27 are not used without depending on the ePDCCHassignment. Accordingly, for example, base station 100 easily assignsthe PUCCH resources corresponding to eCCEs #24, #25, #26, and #27 asexplicit PUCCH resources. The explicit PUCCH resources are PUCCHresources that are indicated in advance by higher layer signaling, andare PUCCH resources that are used instead of implicit resources duringchannel selection, for a relay terminal, or the like when cross carrierscheduling is not performed at the time of CA application.

In the search space 2, the eCCE indexes corresponding to the PRB pairassigned in common with the search space 1 may not be changed to theeCCE indexes of the search space 1 (for example, may be the same as theeCCE indexes of FIG. 9), and only the association of the eCCE indexesand the PUCCH resources may be the same in the search space 1 and thesearch space 2. For example, the PUCCH resources associated with eCCEs#24, #25, #26, and #27 corresponding to PRB pair #20 in common with thesearch space 1 among eCCEs #16 to #32 assigned to the search space 2 maybe the same as the PUCCH resources associated with eCCEs #12, #13, #14,and #15 corresponding to PRB pair #20 of the search space 1.

Embodiment 3

In the present embodiment, a case where distributed assignment isapplied to an ePDCCH will be described. A base station and a terminalaccording to the present embodiment share the same basic configurationas base station 100 and terminal 200 according to Embodiment 1.Accordingly, description will be provided referring back to FIGS. 7 and8.

In the distributed assignment, an eCCE is assigned to a plurality of PREpairs. Specifically, one eCCE is assigned to a plurality of eREGs(resources obtained by dividing a PRB pair) that belong to different PRBpairs. The number of divisions (the number of eREGs per PRB pair) of aPRB pair may be 8, 12, 16, 24, 36, and the like. When the size of aresource to which one eCCE is assigned corresponds to a resource that isobtained by dividing a PRB pair into four parts, and when a PRB pair isdivided into 8, 12, 16, 24, and 36 parts, one eCCE may be divided into2, 3, 4, 6, and 9 parts and assigned to different PRB pairscorresponding to the number of divisions of the eCCE distributedassignment in a distributed manner. The number of divisions of the eCCEmay be referred to as an eCCE diversity order.

For example, as illustrated in FIG. 12, when a PRB pair is divided into8 parts, the number of eREGs per PRB pair is 8, and one eCCE is dividedinto two parts and assigned to two eREGs of different PRB pairs. In FIG.12, distributed assignment is made to two PRB pairs in units of eCCEs #Nto #N+7 (in FIG. 12, N=0, 8) in a distributed manner. For example, asillustrated in FIG. 12, eCCEs #0 to #7 are assigned to PRB pair #A andPRB pair #C, eCCEs #8 to #15 are assigned to PRB pair #B and PRB pair#D.

Similarly, for example, as illustrated in FIG. 13, when a PRB pair isdivided into 16 parts, the number of eREGs per PRB pair is 16, and oneeCCE is divided into 4 parts and assigned to four eREGs of different PRBpairs. In FIG. 13, distributed assignment is made to four PRB pairs inunits of eCCEs #N to #N+15 (in FIG. 13, N=0). For example, asillustrated in FIG. 13, eCCEs #0 to #15 are assigned to PRB pairs #A,#B, #C, and #D.

As described above, in the distributed assignment, one eCCE is assignedto a plurality of PRB pairs. As in Embodiment 1, a plurality of searchspaces (search space 1 and search space 2) may be configured for oneterminal 200, and as in Embodiment 2, the same PRB pair may be assignedin common among a plurality of search spaces configured in one terminal200. Accordingly, in the present embodiment, when there is a PRB pairassigned to the search space 1 and the search space 2 in an overlappingmanner among a plurality of PRB pairs to which any eCCE of each searchspace is assigned, base station 100 and terminal 200 makes the eCCEindexes of the search space 2 corresponding to the PRB pair the same asthe eCCE indexes of the search space 1.

Hereinafter, as an example, a search space configuration method when thenumber of divisions of a PRB pair is 8 (eCCE diversity order: 2) and 16(eCCE diversity order: 4) will be described referring to FIGS. 14 and15.

In FIGS. 14 and 15, a search space 1 (SS1) and a search space 2 (SS2)are configured in UE1.

<When the Number of Divisions is 8 (FIG. 14)>

In FIG. 14, the search space 1 is assigned to PRB pairs #2, #8, #14, and#20, and the search space 2 is assigned to PRB pairs #0, #10, #16, and#20. That is, PRB pair #20 is assigned in an overlapping manner in thesearch space 1 and search space 2.

UE1 first allocates the eCCE indexes (eCCE #8 to eCCE #15) to 16 eCCEsof the search space 1. Accordingly, eCCE #0 to eCCE #7 of the searchspace 1 are assigned to PRB pairs #2 and #14, and eCCE #8 to eCCE #15 ofthe search space 1 are assigned to PRB pairs #8 and #20.

Next, UE1 determines the eCCE indexes of the search space 2. Acombination of PRB pairs #10 and #20 as the PRB pairs assigned to thesearch space 2 includes PRB pair #20 assigned to the search space 1.Accordingly, UE1 allocates the eCCE indexes (eCCE #8 to eCCE #15)corresponding to PRB pairs #8 and #20 as a combination including PRBpair #20 of the search space 1 as the eCCE indexes of the search space 2corresponding to PRB pairs #10 and #20.

A combination of PRB pairs #0 and #16 as the PRB pairs assigned to thesearch space 2 does not include the PRB pairs assigned to the searchspace 1. Accordingly, UE1 newly allocates the CCE indexes (eCCE #16 toeCCE #23) to PRB pairs #0 and #16.

<When the Number of Divisions is 16 (FIG. 15)>

In FIG. 15, the search space 1 is assigned to PRB pairs #2, #8, #14, and#20, and the search space 2 is assigned to PRB pairs #0, #8, #16, and#20. That is, PRB pairs #8 and #20 are assigned in an overlapping mannerin the search space 1 and the search space 2.

UE1 first allocates the eCCE indexes (eCCE #0 to eCCE #15) to 16 eCCEsof the search space 1 in an ascending order. Accordingly, eCCE 0 to eCCE#15 of the search space 1 are assigned to PRB pairs #2, #8, #14, and#20.

Next, UE1 determines the eCCE indexes of the search space 2. Acombination of PRB pairs #0, #8, #16, and #20 assigned to the searchspace 2 includes PRB pairs #8 and #10 assigned to the search space 1.Accordingly, UE1 allocates the same eCCE indexes as the CCE indexes(eCCE #0 to eCCE #15) of the search space 1 as the eCCE indexes of thesearch space 2.

In this way, base station 100 and terminal 200 allocate the same eCCEindexes as specific eCCEs to eCCEs, in which at least one PRB pair amonga plurality of assigned PRB pairs is the same as a PRB pair assigned tospecific eCCEs among a plurality of eCCEs of the search space 1, among aplurality of eCCEs of the search space 2. Base station 100 and terminal200 allocate the eCCE indexes larger than the eCCE indexes of the searchspace 1 to the eCCEs other than the eCCEs, to which the same eCCEindexes as the specific eCCEs are allocated, among a plurality of eCCEsof the search space 2.

As described above, in the distributed assignment, an eCCE is assignedto a plurality of PRB pairs in eCCE units (for example, when a PRB pairis divided into 8 parts, in units of 8 eCCEs, and when a PRB pair isdivided into 16 parts, in units of 16 eCCEs) corresponding to the numberof divisions of a PRB pair in a distributed manner. Accordingly, asillustrated in FIG. 14 or 15, in the search space 2, the eCCEs to whichthe same eCCE indexes as the eCCE indexes of the search space 1 are inunits of eCCEs corresponding to the number of divisions of a PRB pair.

In this way, even when the distributed assignment is applied to thesearch space 1 and the search space 2, when the overlapping PRB pair isassigned to a plurality of search spaces, the eCCE indexes correspondingto the PRB pair are the same between a plurality of search spaces.Accordingly, it is possible to reduce the total number of eCCE indexesof the entire search space (SS1 and SS2) configured in terminal 200, andto reduce the number of PUCCH resources corresponding to the eCCEindexes. Therefore, since it is also possible to reduce the number ofPUCCH resources associated with the eCCEs, throughput in the uplink isimproved.

In the present embodiment, the distributed assignment in the frequencydomain has been described, a domain to which the distributed assignmentis applied may be a time domain or a frequency-time domain.

Embodiment 4

In the present embodiment, a case where localized assignment anddistributed assignment are mixedly applied in a plurality of ePDCCHsearch spaces that are configured in a terminal will be described. Abase station and a terminal according to the present embodiment sharethe same basic configuration as base station 100 and terminal 200according to Embodiment 1. Accordingly, description will be providedreferring back to FIGS. 7 and 8.

The reason for mixing the localized assignment and the distributedassignment is to reduce the total number of PRB pairs to be used for anePDCCH while selecting an assignment method (localized assignment anddistributed assignment) for each terminal.

However, it is necessary to maintain the characteristic that, in thelocalized assignment, ePDCCHs are collectively assigned at positionsclose to each other on a frequency domain, and in the distributedassignment, ePDCCHs are assigned on a frequency domain in a distributedmanner. In the distributed assignment, it is necessary to assign thesame eCCE to different resources (eREGs) of each PRB pair, therebyaveraging channel estimation precision and power per OFDM symbol. Thecharacteristic of channel estimation precision is degraded as being awayfrom a reference signal (RS). Since there is a restriction to power ofthe OFDM symbol value, if there are variations in OFDM symbols to beassigned, power boosting is not easily performed.

In this way, an assignment rule of a PRB pair to an eCCE varies in thelocalized assignment and the distributed assignment.

FIGS. 16A and 16B illustrate an example of the correspondencerelationship of the eCCE indexes (FIG. 16A) and the PRB pairs (FIG. 16B)when the localized assignment and the distributed assignment are mixedlyapplied. In FIG. 16A, the distributed assignment is applied to thesearch space 1 (SS1), and the localized assignment is applied to thesearch space 2 (SS2). Hereinafter, the eCCEs of the search space 1 towhich the distributed assignment is applied are simply referred to as“distributed eCCEs”, and the eCCEs of the search space 2 to which thelocalized assignment is applied are simply referred to as “localizedeCCEs”.

In FIG. 16A, eCCE #0 to eCCE #15 are allocated to 16 eCCEs of the searchspace 1. In FIG. 16A, since 16 eCCEs of the search space 2 are assignedto the same PRB pairs #A to #D as the 16 eCCEs of the search space 1,eCCE #0 to eCCE #15 that are the same eCCE indexes as the 16 eCCEs ofthe search space 1 are assigned to the 16 eCCEs of the search space 2.

The same association of the eCCE indexes and the PUCCH resources (forexample, see FIG. 3) is applied to both the distributed eCCEs and thelocalized eCCEs.

Each block illustrated in FIG. 16B represents an eREG; and a numeralwithin the block represents a distributed eCCE index (see FIG. 16A) thatis assigned to the eREG. That is, in FIG. 16B, a PRB pair is dividedinto 16 eREGs, and one distributed eCCE is assigned to four PRB pairs.As shown in FIG. 16B, in the distributed assignment, different eREGs areused for each PRB pair. However, the arrangement of actual physicalresources of eREGs is not limited to FIG. 16B, and REs included in aneREG are separately defined in advance.

In FIG. 16B, 4 localized CCEs are assigned per PRB pair. For example,localized eCCE #3 illustrated in FIG. 16A is assigned to the uppermostresources (the same resources as four eREGs corresponding to distributedeCCEs #3, #7, #11, and #15) of the PRB pair #A. Similarly, localizedeCCE #7 illustrated in FIG. 16A is assigned to the uppermost resources(the same resources as four eREGs corresponding to distributed eCCEs#15, #6, #14, and #7) of PRB pair #B. The same applies to otherlocalized eCCEs.

Locations surrounded by four kinds of rectangles in the search space 2(localized assignment is applied) illustrated in FIG. 16A representdistributed eCCEs (in FIG. 16A, representing only distributed eCCEs #3,#7, #11, and #15 of the search space 1) in a PRB pair against which therespective localized eCCEs collide. For example, localized eCCE #7 ofthe search space 2 collides against distributed eCCEs #7 and #15 of thesearch space 1 in a PRB pair. Similarly, localized eCCE #8 collidesagainst distributed eCCE #3 in a PRB pair. The same applies to otherlocalized eCCEs.

Two kinds of filled regions in the search space 1 (distributedassignment is applied) illustrated in FIG. 16A represent the distributedeCCEs in a FRB pair against which the localized eCCEs #3 and #7 collide.For example, localized eCCE #3 of the search space 2 collides againstdistributed eCCEs #3, #7, #11, and #15 of the search space 1 in a PRBpair. Similarly, localized eCCE #7 collides against distributed eCCEs#6, #7, #14, and #15 in a PRB pair.

As shown in FIGS. 16A and 16B, when localized eCCE #3 is used forterminal 200, distributed eCCEs #3, #7, #11, and #15 which collideagainst each other in a PRB pair when being simultaneously used cannotbe used. If distributed eCCEs #3, #7, #11, and #15 are not used, whilelocalized eCCE #3 is usable, the localized eCCEs to which eCCE indexes(eCCEs #7, #11, and #15) other than eCCE #3 are assigned cannot be used.For example, even when distributed eCCEs #3, #7, #11, and #15 are notused, in order to use localized eCCE #7, it is necessary to newly avoidthe use of distributed eCCEs #6 and #14.

That is, in FIGS. 16A and 16B, while the use of localized eCCE #3 islimited (blocked) by distributed eCCEs #3, #7, #11, and #15, the use oflocalized eCCE #7 is limited (blocked) by distributed eCCEs #6, #7, #14,and #15. This is because eCCE indexes do not match and are separatedbetween distributed eCCE that are blocked by a localized eCCE andlocalized eCCEs that are blocked by a distributed eCCE. Specifically, inFIGS. 16A and 16B, while localized eCCE #3 limits (blocks) the use ofdistributed eCCEs #3, #7, #11, and #15, distributed CCE #3 limits theuse of localized eCCEs #3, #5, #8, and #14. Similarly, while localizedeCCE #7 limits (blocks) the use of distributed eCCEs #6, #7, #14, and#15, distributed CCE #7 limits the use of localized eCCEs #3, #7, #9,and #14.

In this way, in an example illustrated in FIGS. 16A and 16B, a localizedeCCE against which a distributed eCCE collides and a distributed eCCEagainst which a localized eCCE collides have no regularity, and thereare variations in eCCEs (eCCEs to be blocked) that cannot be used byeCCEs selected in a search space to which one assignment method isapplied. Accordingly, if the association of both a distributed eCCE anda localized CCE with the same PUCCH resource (for example, see FIG. 3)is applied, there are variations in the limits (blocking) to the use ofthe PUCCH resources that are associated with the eCCEs assigned bothsearch spaces, and the utilization efficiency of the PUCCHs is degraded.

Since a distributed eCCE is distributed and assigned to M PRB pairs, atleast M localized eCCEs are blocked by any distributed eCCE. Since alocalized eCCE is assigned to resources corresponding to M eREGs, Mdistributed eCCEs are blocked by any localized eCCE. The association ofboth a distributed eCCE and a localized CCE with the same PUCCH resource(for example, see FIG. 3) is applied.

Accordingly, in the present embodiment, eCCE assignment such thatcollision occurs in units of M eCCEs in a PRB pair is defined betweenthe localized assignment and the distributed assignment. M representsthe number of divisions (eCCE diversity order) in which an eCCE isdivided during the distributed assignment. For example, when the numberof divisions of a PRB pair is 8, 12, 16, 24, and 36, M=2, 3, 4, 6, and9.

Specifically, in the present embodiment, base station 100 and terminal200 assign the resources, to which specific M localized eCCEs areassigned, to the same resources as the resources to which M distributedeCCEs (that is, distributed eCCEs that block the M localized eCCEs), towhich the same eCCE indexes as the M localized eCCEs are allocated, areassigned. That is, when the localized assignment and the distributedassignment are mixedly applied in the search space 1 and the searchspace 2 configured in terminal 200, specific localized eCCEscorresponding to the number of a plurality of PRB pairs (M PRB pairs) towhich distributed eCCEs are distributed and assigned are assigned to thesame resources (RE) as the eREGs to which distributed eCCEs, to whichthe same eCCE indexes as the specific localized eCCEs are allocated, areassigned.

For example, base station 100 and terminal 200 assign localized eCCEs#N, #N+4, #N+8, and #N+12 to the resources (eREGs) to which distributedeCCEs #N, #N+4, #N+8, and #N+12 are assigned. That is, in thedistributed assignment and the localized assignment, the eCCEscorresponding to the number of divisions M when dividing an eCCE areassigned to the same resource.

FIGS. 17A and 17B illustrate the correspondence relationship betweeneCCE indexes (FIG. 17A) and PRB pairs (FIG. 17B) in the presentembodiment. In FIG. 17B, similarly to FIG. 16B, four localized CCEindexes are assigned per PRB pair. In FIG. 17B, similarly to FIG. 16B, aPRB pair is divided into 16 eREGs, and the number of divisions (eCCEdiversity order) of an eCCEs in the distributed assignment is 4 (M=4).In FIG. 17A, as in Embodiment 2, the same PRB pairs #A to #D areassigned in the search space 1 and the search space 2, and the same eCCEindexes (eCCEs #0 to #15) are allocated to both search spaces.

In FIGS. 17A and 17B, the assignment of distributed eCCEs in a PRB pairis the same as in FIG. 16B. That is, in FIG. 17B, distributed eCCEs #3,#7, #11, and #15 are assigned to the resources (eREGs) within the PRBpairs #A, #B, #C, and #D, and the position of the resource (eREG) variesfor each PRB pair.

Localized eCCEs #3, #7, #11, and #15 are assigned to the resources(eREGs), to which distributed eCCEs #3, #7, #11, and #15 are assigned,in PRB pairs #A, #B, #C, and #D. For example, localized eCCE #7 isassigned to the same resources as four eREGs corresponding todistributed eCCEs #3, #7, #11, and #15 in PRB pair #B. Similarly,localized eCCE #11 is assigned to the same resources as four eREGscorresponding to distributed eCCEs #3, #7, #11, and #15 in PRB pair #C.The same applies to localized eCCEs #3 and #15.

With this, the eCCE indexes of M distributed eCCEs that are blocked byany localized eCCE match M localized eCCE indexes that are blocked bylocalized eCCEs having the same eCCE indexes as distributed eCCEs havingthe same eCCE indexes as the localized eCCEs. For example, in FIGS. 17Aand 17B, localized eCCE #3 (or #7, #11, #15) blocks distributed eCCEs#3, #7, #11, and #15, and distributed eCCE #3 (or #7, #11, #15) blockslocalized eCCEs #3, #7, #11, and #15.

Accordingly, the number of localized eCCEs that cannot be used (areblocked) by a distributed eCCE can be limited to M. As described above,since M corresponds to the number of PRB pairs in which distributedeCCEs are distributed and arranged, at least M localized eCCEs areblocked by the use of any distributed eCCE. That is, according to thepresent embodiment, it is possible to minimize the number of localizedeCCEs that are cannot be used by a distributed eCCE. Accordingly, it ispossible to minimize the number of PUCCH resources to be blocked.

In FIGS. 17A and 17B, although the case of localized eCCEs #3, #7, #11,and #15 and distributed eCCEs #3, #7, #11, and #15 (that is, N=3) hasbeen described, the same applies to other eCCEs (N=0, 1, 2).

In this way, in the present embodiment, the resources within a PRB pairto which the same eCCE indexes are assigned are shared by the localizedassignment and the distributed assignment. Accordingly, while theassignment rule of an eCCE in a PRB pair varies in the localizedassignment and the distributed assignment, collision of eCCE indexes andcollision of PUCCH resources match each other. Therefore, according tothe present embodiment, wasteful resource assignment in a PUCCH isreduced, thereby improving the utilization efficiency of the PUCCHs.

For example, base station 100 configures the search space 1 and thesearch space 2 for each terminal 200, and easily switches between thedistributed assignment and the localized assignment based on the channelquality of each terminal 200, reliability of feedback information, orthe like.

In the present embodiment, a case where different assignment methods areapplied to a plurality of search spaces configured in one terminal 200has been described. However, the present embodiment is not limitedthereto, and for example, is effective for a case where the distributedassignment is applied to UE1, the localized assignment is applied toUE2, and the PRB pairs corresponding to the eCCEs of the respectivesearch spaces are the same.

In the present embodiment, a case where a PRB pair is divided into 16parts (M=4) has been described, the present invention is not limitedthereto. For example, when a PRB pair is divided into 8 parts (M=2),base station 100 and terminal 200 arrange localized eCCEs #N and #N+4 inthe resources to which distributed eCCEs #N and #N+4 are assigned. FIGS.18A and 18B illustrate a search space configuration example when M=2. InFIGS. 18A and 18B, distributed eCCEs #3 and #7 are assigned to PRB pairs#A and #C, and the position of the resource (eREG) varies for each PRBpair. Localized CCEs #3 and #7 are assigned to the resources, to whichdistributed eCCEs #3 and #7 are assigned, in PRB pairs #A and #C. Thatis, in the distributed assignment and the localized assignment, theeCCEs corresponding to the number of divisions M=2 when dividing an eCCEare assigned to the same resource. With this, it is possible to limitthe number of localized eCCEs whose use is limited (blocked) by adistributed eCCE, and to limit the number of PUCCH resources to beblocked. For example, localized eCCE #3 blocks only distributed eCCEs #3and #7, and distributed eCCE #3 blocks only localized eCCEs #3 and #7.Similarly, localized eCCE #7 blocks only distributed eCCEs #3 and #7,and distributed eCCE #7 blocks only localized eCCEs #3 and #7.

As in Embodiment 2 (FIG. 10), when the same PRB pair is assigned to someeCCEs between a plurality of search spaces configured in one terminal200, and different PRB pairs are individually assigned to other eCCEs(for example, see FIGS. 19A and 19B), as in the present embodiment, thesame resources as distributed eCCEs (distributed eCCEs #3, #7, #11, and#15) that are blocked by localized eCCEs are assigned to the localizedeCCEs (localized eCCEs #3, #7, and #11) to which a PRB pair is assigned,and resources of an individual PRB pair (PRB pair #D′) are assigned tolocalized eCCEs (localized eCCEs #16 to #19) that are assigned to thedifferent PRB pairs. In this way, in the localized eCCEs assigned todifferent PRB pairs, the eCCEs can be used to transmit the ePDCCHwithout taking into consideration collision with distributed eCCEs.

In the present embodiment, the distributed assignment and the localizedassignment in the frequency domain have been described, a domain towhich the distributed assignment and the localized assignment areapplied may be a time domain or a frequency-time domain.

The foregoing describes the embodiments of the present invention.

Other Embodiments

[1] In the foregoing embodiments, a case where one search space includes16 eCCEs has been described. However, the number of eCCEs included inone search space is not limited to 16. The number of PRB pairs and thenumber of eCCEs may vary in the search space 1 and the search space 2that are configured in one terminal.

[2] In the foregoing embodiments, although a case where implicitresources of a PUCCH are defined by the association of eCCE indexes andPUCCH resources has been described, instead of the eCCE indexes, eREGindexes may be used.

[3] As a way to change the implicit assignment method by the associationwith eCCE indexes and PUCCH resources to a different assignment method,there are (1) a method of giving notification of the start position ofthe PUCCH resource for each terminal or each search space, (2) a methodof giving notification of ART (ACK/NACK Resource Indicator) with a DLassignment and adding a shift amount corresponding to the ARI to theimplicit resources of the PUCCH, and (3) a method of using explicitresources corresponding to the ARI, and these methods can be used alongwith the foregoing embodiments. For example, as in the method (1), whenthe start position of the PUCCH resource varies for each search space,in a PRB pair that is shared in the search space 1 and the search space2, the start position of the PUCCH resource of the search space 1 may benotified. As in the method (2), when giving notification of the shiftamount with the ARI, as the shift amount, a shift amount of a PUCCH maybe defined or a shift amount of an eCCE index may be defined.

[4] In the foregoing embodiments, although a case where an ePDCCH searchspace is configured has been described, the above-described search spaceconfiguration method can be applied to a R-PDCCH which is a controlsignal for relay, instead of an ePDCCH.

[5] The term “antenna port” refers to a logical antenna including one ormore physical antennas. In other words, the term “antenna port” does notnecessarily refer to a single physical antenna, and may sometimes referto an array antenna including a plurality of antennas, and/or the like.

For example, how many physical antennas are included in the antenna portis not defined in LTE, but the antenna port is defined as the minimumunit allowing the base station to transmit different reference signalsin LTE.

In addition, an antenna port may be specified as a minimum unit to bemultiplied by a precoding vector weighting.

[6] In the foregoing embodiments, the present invention is configuredwith hardware by way of example, but the invention may also be providedby software in cooperation with hardware.

In addition, the functional blocks used in the descriptions of theembodiments are typically implemented as LSI devices, which areintegrated circuits. The functional blocks may be formed as individualchips, or a part or all of the functional blocks may be integrated intoa single chip. The term “LSI” is used herein, but the terms “IC,”“system LSI,” “super LSI” or “ultra LSI” may be used as well dependingon the level of integration.

In addition, the circuit integration is not limited to LSI and may beachieved by dedicated circuitry or a general-purpose processor otherthan an LSI. After fabrication of LSI, a field programmable gate array(FPGA), which is programmable, or a reconfigurable processor whichallows reconfiguration of connections and settings of circuit cells inLSI may be used.

Should a circuit integration technology replacing LSI appear as a resultof advancements in semiconductor technology or other technologiesderived from the technology, the functional blocks could be integratedusing such a technology. Another possibility is the application ofbiotechnology and/or the like.

A base station apparatus according to the embodiments described aboveincludes: a configuration section that configures, within a dataassignable region for a terminal apparatus, a first search space and asecond search space each being a candidate to which control informationis assigned, each of the first search space and the second search spaceincluding a plurality of control channel elements; and a transmissionsection that transmits the control information assigned to each of thefirst search space and the second search space, in which: a number of acontrol channel element to which the control information is assigned isassociated on a one-to-one basis with an uplink resource to be used totransmit a response signal to downlink data; and the configurationsection allocates numbers to a plurality of first control channelelements included in the first search space in an ascending order, andallocates numbers larger than or identical with the numbers allocated tothe first control channel elements to a plurality of second controlchannel elements included in the second search space.

In the base station apparatus according to the embodiments, theplurality of control channel elements are respectively assigned tophysical resources; and the configuration section allocates a numberidentical with a third control channel element among the plurality offirst control channel elements to a fourth control channel elementassigned to a physical resource identical with a physical resource towhich the third control channel element is assigned, among the pluralityof second control channel elements, and allocates a number larger thanthe numbers allocated to the plurality of first control channel elementsto a control channel element other than the fourth control channelelement among the plurality of second control channel elements.

In the base station apparatus according to the embodiments: theplurality of control channel elements are assigned to a plurality ofphysical resources distributed in a frequency domain; and theconfiguration section allocates a number identical with a third controlchannel element among the plurality of first control channel elements toa fourth control channel element assigned to physical resourcesincluding at least one physical resource that is identical with aphysical resource assigned to the third control channel element, amongthe plurality of second control channel elements, and allocates a numberlarger than the numbers allocated to the plurality of first controlchannel elements to a control channel element other than the fourthcontrol channel element among the plurality of second control channelelements.

In the base station apparatus according to the embodiments: a pluralityof control channel elements included in one of the first search spaceand the second search space are assigned to a single physical resourcein a frequency domain, and a plurality of control channel elementsincluded in the other one of the search spaces are assigned to aplurality of physical resources distributed in the frequency domain; anumber of resource elements included in the single physical resource isequal to a total number of resource elements included in the pluralityof physical resources; and specific control channel elementscorresponding to the number of the plurality of physical resources inthe one of the search spaces are assigned to resource elements identicalwith resource elements to which the control channel elements of theother one of the search spaces are assigned, the control channelelements of the other one of the search spaces being allocated a numberidentical with the specific control channel elements.

In the base station apparatus according to the embodiments, the firstsearch space is a search space that is shared by a plurality of terminalapparatuses, and the second search space is a search space that isindividually configured for each of the terminal apparatuses.

In the base station apparatus according to the embodiments, the firstsearch space and the second search space are each a search spaceindividually configured for the terminal apparatus, and the first searchspace is used with priority over the second search space.

In the base station apparatus according to the embodiments:communication with the terminal apparatus is performed using a pluralityof component carriers (CCs) including a primary cell and one or moresecondary cells; and the first search space is a search space to whichcontrol information for a primary cell is assigned, and the secondsearch space is a search space to which control information for asecondary cell is assigned.

A terminal apparatus according to the embodiments described aboveincludes: a configuration section that configures, within a dataassignable region, a first search space and a second search space eachbeing a candidate to which control information is assigned, each of thefirst search space and the second search space including a plurality ofcontrol channel elements; and a reception section that receives thecontrol information assigned to each of the first search space and thesecond search space, in which: a number of a control channel element towhich the control information is assigned is associated on one-to-onebasis with an uplink resource to be used to transmit a response signalto downlink data; and the configuration section allocates numbers to aplurality of first control channel elements included in the first searchspace in an ascending order, and allocates numbers larger than oridentical with the numbers allocated to the first control channelelements to a plurality of second control channel elements included inthe second search space.

In the terminal apparatus according to the embodiments: the plurality ofcontrol channel elements are respectively assigned to physicalresources, and the configuration section allocates a number identicalwith a third control channel element among the plurality of firstcontrol channel elements to a fourth control channel element assigned toa physical resource identical with a physical resource to which thethird control channel element is assigned among the plurality of secondcontrol channel elements and allocates a number larger than the numbersallocated to the plurality of first control channel elements to acontrol channel element other than the fourth control channel elementamong the plurality of second control channel elements.

In the terminal apparatus according to the embodiments: the plurality ofcontrol channel elements are assigned to a plurality of physicalresources distributed in a frequency domain; and the configurationsection allocates a number identical with a third control channelelement among the plurality of first control channel elements to afourth control channel element assigned to physical resources includingat least one physical resource that is identical with a physicalresource assigned to the third control channel element, among theplurality of second control channel elements, and allocates a numberlarger than the numbers allocated to the plurality of first controlchannel elements to a control channel element other than the fourthcontrol channel element among the plurality of second control channelelements.

In the terminal apparatus according to the embodiments: a plurality ofcontrol channel elements included in one of the first search space andthe second search space are assigned to a single physical resource in afrequency domain, and a plurality of control channel elements includedin the other one of the search spaces are assigned to a plurality ofphysical resources distributed in the frequency domain; a number ofresource elements included in the single physical resource is equal to atotal number of resource elements included in the plurality of physicalresources; and specific control channel elements corresponding to thenumber of the plurality of physical resources in the one of the searchspaces are assigned to resource elements identical with resourceelements to which the control channel elements of the other one of thesearch spaces are assigned, the control channel elements of the otherone of the search spaces being allocated a number identical with thespecific control channel elements.

In the terminal apparatus according to the embodiments, the first searchspace is a search space that is shared by a plurality of terminalapparatuses, and the second search space is a search space that isindividually configured for each of the terminal apparatuses.

In the terminal apparatus according to the embodiments, the first searchspace and the second search space are each a search space that isindividually configured for the terminal apparatus, and the first searchspace is used with priority over the second search space.

In the terminal apparatus according to the embodiments: communicationwith the terminal apparatus is performed using a plurality of componentcarriers (CCs) having a primary cell and one or more secondary cells;and the first search space is a search space to which controlinformation for a primary cell is assigned, and the second search spaceis a search space to which control information for a secondary cell isassigned.

A transmission method according to the embodiments described aboveincludes: configuring, within a data assignable region for a terminalapparatus, a first search space and a second search space each being acandidate to which control information is assigned, each of the firstsearch space and the second search space including a plurality ofcontrol channel elements; and transmitting the control informationassigned to each of the first search space and the second search space,in which: a number of a control channel element to which the controlinformation is assigned is associated on a one-to-one basis with anuplink resource to be used to transmit a response signal to downlinkdata; and numbers are allocated to a plurality of first control channelelements included in the first search space in an ascending order, andnumbers larger than or identical with the numbers allocated to the firstcontrol channel elements are allocated to a plurality of second controlchannel elements included in the second search space.

A reception method according to the embodiments described aboveincludes: configuring, within a data assignable region for a terminalapparatus, a first search space and a second search space each being acandidate to which control information is assigned, each of the firstsearch space and the second search space including a plurality ofcontrol channel elements; and receiving the control information assignedto each of the first search space and the second search space, in which:a number of a control channel element to which the control informationis assigned is associated on a one-to-one basis with an uplink resourceto be used to transmit a response signal to downlink data; and numbersare allocated to a plurality of first control channel elements includedin the first search space in an ascending order, and numbers larger thanor identical with the numbers allocated to the first control channelelements are allocated to a plurality of second control channel elementsincluded in the second search space.

The disclosure of Japanese Patent Application No. 2012-164619, filed onJul. 25, 2012, including the specification, drawings and abstract areincorporated herein by reference in its entirety.

INDUSTRIAL APPLICABILITY

The present invention is useful in that, even when a plurality of ePDCCHsearch spaces are configured for a single terminal, it is possible toavoid collision of PUCCH resources between terminals.

REFERENCE SIGNS LIST

-   100 Base station-   200 Terminal-   101 Assignment information generation section-   102, 205 Configuration section-   103, 207 Error correction coding section-   104, 208 Modulation section-   105, 209 Signal assignment section-   106, 210 Transmission section-   107, 201 Reception section-   108, 203 Demodulation section-   109, 204 Error correction decoding section-   110 A/N signal demodulation section-   202 Signal separation section-   206 Control signal reception section

The invention claimed is:
 1. A communication apparatus comprising:circuitry, which, in operation: configures at least one of (i) a firstsearch space for localized transmission, which is comprised of aplurality of first control channel elements (CCEs), each first CCEconsisting of four enhanced resource element groups (EREGs) in onephysical resource block pair (PRB pair), and (ii) a second search spacefor distributed transmission, which is comprised of a plurality ofsecond CCEs, each second CCE consisting of four EREGs distributed amonga plurality of PRB pairs, wherein each of the one or the plurality ofPRB pairs is divided into sixteen EREGs; and maps assignment informationto at least one of the first search space and the second search space;and a transmitter, which, in operation, transits the assignmentinformation and PRB pair information related to the PRB pairs to aterminal, the PRB pair information being used at the terminal to specifya configuration of at least one of the first search space and the secondsearch space, wherein four EREGs that are provided in one PRB pair,which form a portion of EREGs that correspond to a subset of theplurality of second CCEs, are identical to four EREGs that correspond toone first CCE of a subset of the plurality of first CCEs, and four EREGsthat are provided in another PRB pair, which form another portion of theEREGs that correspond to said subset of the plurality of second CCEs,are identical to four EREGs that correspond to another first CCE of saidsubset of the plurality of first CCEs.
 2. The communication apparatusaccording to claim 1, wherein the subset of the plurality of first CCEsis comprised of four first CCEs and the subset of the plurality ofsecond CCEs is comprised of four second CCEs.
 3. The communicationapparatus according to claim 1, wherein said circuitry, in operation,configures the plurality of PRB pairs as the first search space or thesecond search space, and the plurality of first CCEs or the plurality ofsecond CCEs, which constitute the plurality of PRB pairs, aresequentially numbered from zero.
 4. The communication apparatusaccording to claim 1, wherein said circuitry, in operation, configuresfirst PRB pairs defining the first search space and second PRB pairsdefining the second search space, the plurality of first CCEsconstituting the first PRB pairs are sequentially numbered from zero,and the plurality of second CCEs constituting the second PRB pairs aresequentially numbered from zero.
 5. The communication apparatusaccording to claim 1, wherein one second CCE corresponds to differentEREGs in different PRB pairs.
 6. The communication apparatus accordingto claim 1, wherein at least one of the first search space and thesecond search space is configured in a physical downlink shared channel(PDSCH) region, each of the plurality of first CCEs and the plurality ofsecond CCEs is an enhanced CCE (ECCE), and the assignment information istransmitted on an enhanced physical downlink control channel (EPDCCH).7. A communication method performed by circuitry, the communicationmethod comprising: configuring at least one of (i) a search space forlocalized transmission, which is comprised of a plurality of firstcontrol channel elements (CCEs), each first CCE consisting of fourenhanced resource element groups (EREGs) in one physical resource blockpair (PRB pair), and (ii) a second search space for distributedtransmission, which is comprised of a plurality of second CCEs, eachsecond CCE consisting of four EREGs distributed among a plurality of PRBpairs, wherein each of the one or the plurality of PRB pairs is dividedinto sixteen EREGs; mapping assignment information to at least one ofthe first search space and the second search space; and transmitting theassignment information and PRB pair information related to the PRB pairsto a terminal, the PRB pair information being used at the terminal tospecify a configuration of at least one of the first search space andthe second search space, wherein four EREGs that are provided in one PRBpair, which form a portion of EREGs that correspond to a subset of theplurality of second CCEs, are identical to four EREGs that correspond toone first CCE of a subset of the plurality of first CCEs, and four EREGsthat are provided in another PRB pair, which form another portion of theEREGs that correspond to said subset of the plurality of second CCEs,are identical to four EREGs that correspond to another first CCE of saidsubset of the plurality of first CCEs.
 8. The communication methodaccording to claim 7, wherein the subset of the plurality of first CCEsis comprised of four first CCEs and the subset of the plurality ofsecond CCEs is comprised of four second CCEs.
 9. The communicationmethod according to claim 7, wherein the plurality of PRB pairs areconfigured as the first search space or the second search space, and theplurality of first CCEs or the plurality of second CCEs, whichconstitute the plurality of PRB pairs, are sequentially numbered fromzero.
 10. The communication method according to claim 7, wherein firstPRB pairs defining the first search space and second PRB pairs definingthe second search space are configured, the plurality of first CCEsconstituting the first PRB pairs are sequentially numbered from zero,and the plurality of second CCEs constituting the second PRB pairs aresequentially numbered from zero.
 11. The communication method accordingto claim 7, wherein one second CCE corresponds to different EREGs indifferent PRB pairs.
 12. The communication method according to claim 7,wherein at least one of the first search space and the second searchspace is configured in a physical downlink shared channel (PDSCH)region, each of the plurality of first CCEs and the plurality of secondCCEs is an enhanced CCE (ECCE), and the assignment information istransmitted on an enhanced physical downlink control channel (EPDCCH).